Hi
@ceg4048
What exactly do you mean by "poor CO2"? Do you mean the CO2 concentration is below a specific figure and, if so, what is that figure? Or, is it that the CO2 concentration is fluctuating too much and what would you consider to be 'too much'?
I would value your feedback.
JPC
Hi JPC,
The expression "poor CO2" refers to the lack of, or reduced ability of a plant to uptake sufficient quantities of the gas.
Therefore, poor CO2 can occur in the presence of high localized dissolved concentrations of the gas, or it can occur with low concentrations, or in any combination thereof.
Poor CO2 can also occur inside the plant due to an inefficient or ineffective
transport mechanism within the leaf. CO2 has to be transported from outside the leaf to inside the leaf. Then, it has to be transported to the reaction chambers within the leaf in order to be used in the chemical reactions which turn it into sugar. The internal transport mechanism is built around the movement of a complex molecule called RuBisCO, which is an abbreviation for the rather awkward proper name, Ribulose-1,5-bisphosphate carboxylase/oxygenase.
Rubisco is inefficient enzyme even under ideal conditions and is rendered catastrophically ineffective when the leaf is not able to procure sufficient quantities from the water column.
Dissolved gasses move very slowly in water, so it's possible to be pumping in large volumes but yet, not to be delivering the gas to the leaf due to inefficient flow or due to blockage by hardscape or by other leaves.
The reverse can also occur where the amount of gas being injected is relatively low but the distribution of the water is efficient which delivers the gas to the leaf in sufficient quantities.
The worst of these types of cases is where the flow distribution scheme is poorly implemented, the injection rate is low and the demand for CO2 is high due to excessive lighting.
Fluctuations in the delivery of the gas is a more complicated problem. The production of Rubisco is very expensive for the plant. The production rate is controlled by the amount of light as well as the amount of CO2 crossing over from the water through the cell walls. If the plant senses a high traffic of CO2 then it actually
reduces the production rate of Rubisco. Under low CO2 availability, the plant increases the production of Rubisco in order to scavenge as much CO2 as possible. So for example, in a low tech tank, the plants growing there have a higher average Rubisco concentration than the plants growing in a CO2 injected tank.
This works fine for the plants in the high tech tank as they do not need to be efficient at CO2 uptake due to high availability. If the availability decreases however then these plants must suddenly increase the Rubisco production to account for the loss of gas availability. During the time it takes to increase production the plant will suffer a CO2 shortfall since the density of Rubisco is low. It requires almost two weeks to set a new Rubisco production rate so the plant suffers for a while. Now imagine the chaos within the plant if the CO2 levels are constantly changing.
There are so many combinations of these factors that it's easier to sum it all up with the single expression "poor CO2".
Cheers,